Nova (1974–…): Season 41, Episode 11 - Why Sharks Attack - full transcript

From PBS - In recent years, an unusual spate of deadly shark attacks has gripped Australia, resulting in five deaths in 10 months. At the same time, great white sharks have begun appearing ...

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NARRATOR: It's a perfect predator,

acreature that inspires fear and awe.

Because on rare occasions, in the

wrong place at the wrong time.

MAN: I remember this mouth was prolly about 2 feet from me.

NARRATOR: Tragic mistakes are made.

Today many shark populations are falling.

But off the coast of Cape Cod,

sightings of great white sharks are on the rise.

MAN: If you said to me five years ago,

"You're going to tag 34 white sharks in the next four years,"



I'm going to say, "You're out of your mind."

NARRATOR: At the same time, across the seas in Australia,

a sudden spike in fatal shark attacks

has shocked scientists and the community.

Now, shark researchers are unlocking the secrets

of these amazing ancient creatures...

Wow!

NARRATOR: ...to understand the unusual ways

they sense prey

and decipher why sharks have been such effective hunters

for hundreds of millions of years

in an effort to prevent future attacks.

MAN: We really have to understand sharks

to develop effective deterrents.



NARRATOR: Can scientists win the race to save people and sharks?

Right under us, nice shark.

NARRATOR: "Why Sharks Attack," right now on NOVA!

Major funding for NOVA is us, provided by the following:rk.

And the Corporation for Public Broadcasting,

and by PBS viewers like you.

NARRATOR: Cape Cod, Massachusetts,

is a popular summer vacation spot.

And now a new attraction

is drawing tourists to the quaint towns,

pristine beaches and sparkling waters...

Great white sharks.

Even though the 1974 blockbuster Jaws

was filmed in the waters off Cape Cod,

these predators were only rarely seen in the area.

Now, suddenly, they're here, right off the beaches.

How are you?

NARRATOR: Leslie Reynolds is the chief ranger

for the Cape Cod National Seashore,

charged with keeping the public safe.

The arrival of great white sharks

at the height of the summer beach season

is making her job more challenging.

There's already been one attack.

Last year, there was a bite that occurred

at Ballston Beach on a swimmer.

NARRATOR: In 2012, a swimmer was attacked just off shore.

Luckily, he survived with limbs intact.

Keep moving!

NARRATOR: With more sharks showing up,

the chance of another attack is on the rise.

It's really not a matter of if; it's when.

NARRATOR: Greg Skomal is the top shark biologist

for the state of Massachusetts.

His job is to protect sharks and people.

According to records,

the last fatal great white shark attack here was in 1936.

But halfway around the world,

the state of Western Australia has not been so lucky.

An unusual spate of shark attacks over a ten-month period

left five people dead.

September 2011: Kyle Burden, bodyboarding.

October 2011: Bryn Martin,

swimming at Perth's famous Cottlesloe Beach.

NEWSCASTER: The hunt for a killer white pointer.

NARRATOR: And George Wainwright, scuba diver.

March 2012: Peter Kurmann, diving with his brother.

And in July, Ben Linden, surfer.

But it's not just great whites that are a threat.

Other species known to attack humans

are bull sharks, hammerheads,

bronze whalers and tiger sharks.

DAVID PICKERING: You don't feel the teeth.

You don't feel anything.

A bit of pressure, like surgeon steel.

NARRATOR: David Pickering was a snorkeling tour guide

on the reefs of Australia's west coast.

PICKERING: There was three kids with me at the time.

I said, "Guys, I've got a bad feeling.

Stick together."

And I spun around and I remember this mouth

was probably about two feet from me.

The tail sort of kicked out once and it was on me.

I put a hand out like that

and actually cut 13 tendons and all three nerves.

After you've been bitten, the first thing on your mind is,

"Is it coming back for me or someone else?"

Thank God I got bitten and not one of the kids,

because I couldn't live with that.

I can't go out in the water now without thinking about it.

I can't shake that feeling, yeah.

Nervous, anxious...

This is what it reduces me to.

When you love something so much and you can't do it...

I used to take things for granted,

like having a limb that works perfectly.

But now I appreciate every day.

NARRATOR: What triggers sharks to attack humans

when we are not their natural prey?

And can scientists find a way to prevent these tragic events?

12 feet of water.

NARRATOR: Off the coast of Massachusetts,

Greg Skomal says great whites are appearing in waters

where for hundreds of years, they've almost never been seen.

For Skomal, it's a new opportunity to study animals

in the western North Atlantic

whose behavior is virtually unknown.

And if he can track and monitor their movements,

he may be able to lessen the risk to swimmers.

The white shark is probably

the most charismatic fish in the ocean.

White sharks can weigh in excess of 4,000 or 5,000 pounds,

get in excess of 20 feet long, so that's a very big fish.

We know that these sharks can live up to 50 years.

NARRATOR: Great whites are found in every ocean.

Unlike most other sharks,

they produce and store heat in their bodies,

allowing them to tolerate colder temperatures.

In an area where they were rarely seen,

Skomal was surprised to sight and tag a great white shark

off of Cape Cod in 200

Over the next three years, he tagged 17 great whites.

Then, in 2012 alone, he tagged 17 more.

SKOMAL: If you said to me five years ago,

"You're going to tag 34 white sharks in the next four years,"

I'm going to say, "You're out of your mind."

NARRATOR: Why has Cape Cod suddenly become the summer hunting grounds

for one of the ocean's most dangerous predators?

For Skomal, the answer is obvious,

on the beaches and in the water:

seals.

SKOMAL: It wasn't until we had

the development of these seal aggregations here

on the eastern side of Cape Cod

that the white sharks started to take notice.

NARRATOR: The growing number of great whites in the area

seems tied to a population explosion among seals.

SKOMAL: We have several species of seals that occur here,

but the two dominant ones are harbor seals and grey seals.

The grey seal's a much bigger seal species;

it's the one I believe that the white sharks are targeting.

NARRATOR: Seals, a rich, fatty food source for great whites,

once thrived along the northeastern coast

of North America.

But it's believed they were killed

in the hundreds of thousands for their fur, meat and blubber.

SKOMAL: By the end of the 17th century,

Native Americans, early settlers, bounty programs

basically had wiped out the breeding colonies.

And we think that the population had been actually diminished

down to something along the lines of 10,000 animals or less.

NARRATOR: In 1972, the U.S. government

instituted the Marine Mammal Protection Act

prohibiting seal hunting.

Four decades later, seal populations are recovering

and recolonizing old breeding grounds.

SKOMAL: Grey seals get to be

about 700, 800 pounds and eight, nine feet long.

They're big animals.

They're big targets.

Big, thick blubber layer on them.

And now we know

that there's over 300,000 seals off Canada alone

and tens of thousands off the coast of the United States.

It's really ideal habitat for them,

but in them coming here, in essence,

they've opened the café for white sharks.

You've got the perfect zone for white sharks to come in

and consume these animals on a routine basis.

And that's precisely what we've been seeing

over the last decade

as the café emits some kind of delicious odor,

I'm sure, that goes out miles into the Great South Channel.

And once the sharks come in and figure it out,

we've actually had animals come back each year.

NARRATOR: For the seals or anyone swimming near them,

these are potentially dangerous waters.

REYNOLDS: We're just asking that you stay closer to shore,

not swim near seals.

Keep your feet on the ground.

SKOMAL: In the last several years, we've been seeing

more and more evidence of these seals being attacked--

bites on seals, dead seals--

wounds that can really only be created

by one species of fish: you know, the white shark.

NARRATOR: Sometimes, Skomal finds only what's left.

SKOMAL: These are the intestines of a seal.

And that would be really good evidence of an attack.

That's all that's left, which is pretty amazing.

It is ironic that ten miles or so from here

is the set of the movie Jaws.

We talk about Jaws

as this Hollywood production that was fantasy.

And if we look at all the elements of Jaws,

we see, really, many parts of it that are somewhat true.

What Spielberg did was just take those tidbits of truth

and exaggerate the hell out of them.

The white shark getting 20 feet long

becomes the white shark 25 feet long.

The white shark nibbling the boat

becomes the white shark sinking the boat.

The white shark biting people

to the white shark becoming a ravenous predator

desiring human flesh.

All it takes is just one person to be killed in this area,

and that fiction can become reality.

When we have this kind of geographic overlap

between high densities of white sharks

and high densities of people, inevitably we get interactions.

Ise Cod likely to be the next place that happens?

Sure.

This is Shark Cove.

This is the one we get most of the detections on, right?

Right.

NARRATOR: Skomal detects the presence of the sharks he's tagged

over the past four years

with a series of acoustic receivers

suspended in the water.

So number 4.

E-4.

NARRATOR: The tags transmit a signal,

indicating that Skomal's sharks

are returning to their summer hunting grounds.

We've had a shark here today

within the past half-hour.

NARRATOR: This kicks his tagging effort into high gear.

He uses a specially outfitted boat

to sneak up on and tag more sharks.

If Skomal finds sharks close to the beaches,

he can warn beach officials.

SKOMAL: If you've got one 20 meters away just sitting in the water,

you may not know it's there.

NARRATOR: Despite the great white's massive size,

a spotter plane is the best way to find untagged sharks

in the murky green water off the Cape.

SKOMAL: Here we go.

Right up in the shallows, heading for the shore.

See the shadow ahead of you?

There, he's coming back.

Right under us, right under us.

That's our baby!

Nice shark.

NARRATOR: Skomal estimates this great white is nearly 12 feet long,

and it's swimming just a few hundred feet from the beach

in water almost shallow enough for a swimmer to stand.

SKOMAL: Look at it, it's really moving.

NARRATOR: Skomal and the boat's captain

have modified the technique of harpoon fishing for tagging.

SKOMAL: We're able to actually

sneak up on the shark

and place the tag at the base of the dorsal fin.

I'm sure the shark feels it to some degree,

but I always liken it to, perhaps, sneaking up on somebody

and piercing their ear.

Any time one of these sharks swims

within a couple of hundred meters

of one of these receivers,

we get a time stamp on that receiver.

We'll look at it at the end of the year

and get a sense of who's around, when they arrive,

when they leave and where they spend their time.

This will allow us to figure out

whether or not that shark already has a tag in it.

NARRATOR: Skomal uses a hydrophone

that will pick up the telltale acoustic signature

if this shark has already been tagged.

SKOMAL: All right, hydrophones in.

(pinging)

Yeah, 32307.

Tagged it last year.

NARRATOR: He wants to know

how age and sex might determine the shark's movements

and how they're linked to where and what they hunt.

SKOMAL: We've been able to sex

only about half of the sharks we've tagged

because we have great difficulty sexing them

unless we can look underneath them.

We need to tag more fish and have a better sense

of what the boys and girls are doing.

I'd rather be chasing a shark than not.

Beautiful.

You see it, the shadow?

He's turning, he's turning.

Right under us.

NARRATOR: Even this close, it's impossible to determine the sex.

A remote camera offers a solution.

If I can get that pole cam in...

SKOMAL: I say whatever we can get.

Whatever we can get on this fish.

(grunting)

(bleep)

SKOMAL: How you doing, Niko?

Oh, man!

Take a break.

Whoo!

Oh, yeah.

Let's get this other shot right here.

Right there, there you go.

Those are definitely claspers, 100%.

See them right there?

NARRATOR: Claspers are large, long external organs

that male sharks use to mate.

So it's a male.

This is great.

NARRATOR: In just one day, Skomal spots five great whites.

SKOMAL: I see a little boat paint on that fish!

NARRATOR: Some he's tagged in previous years...

SKOMAL: I see one of the tags.

It's red.

NARRATOR: ...and newcomers, too.

Animals that have been elusive can now be studied...

SKOMAL: It's a nice fish.

It's perfectly clean.

NARRATOR: ...as they successfully tag more and more sharks.

SKOMAL: It looks really good.

Let's tag him.

We got it!

NARRATOR: At first, Skomal's tracking data reveals a pattern

linked to the movement of the fish sharks eat

with seasonal changes in water temperature.

SKOMAL: By far, the bulk of the animals move between Cape Cod

and an area between Georgia and northern Florida,

leaving here anywhere from September to December,

arriving in Florida sometime in December.

NARRATOR: Most sharks follow the continental shelf,

moving between the surface and the relatively shallow bottom,

down to a few hundred feet.

SKOMAL: So it was a very simple migratory pattern.

NARRATOR: But some large, mature female great whites

do something very different.

You know, not stay on the shelf, not go to Florida,

go out into the central part of the Atlantic

and start doing deep diving behavior every day

to depths as great as 800 meters, over 2,500 feet.

Very, very, very different

from what we were seeing the other sharks do.

It begs the question: "Why?

"What are you doing?

What are you doing down there?"

NARRATOR: This different pattern for female great whites

is seen in the Pacific Ocean, too.

SKOMAL: What's the big difference?

Well, perhaps they're pregnant.

NARRATOR: Is it possible that they go there to give birth?

SKOMAL: I'm not likely to find out anytime too soon.

All we can really do is hypothesize

that there's some sort of opportunity,

usually driven by reproduction or feeding.

NARRATOR: With every new shark tagged, Skomal learns more.

When one of his tagged sharks returned to Cape Cod

in February, the middle of winter,

it shattered another common assumption.

SKOMAL: We never anticipated they could tolerate

that level of cold water.

So we're getting these new insights into the biology

and in many cases the anatomy of this animal,

how it works physiologically.

I want these animals to survive.

In order to be able to put in place

rules, regulations

that allow for the survival of this species,

we really need to know about the animal

and how it lives from day to day.

NARRATOR: But there are still many unknowns.

SKOMAL: It's pioneering stuff.

It's never been done before.

We never had predictable access to white sharks

in the western North Atlantic.

And because of all those seals sitting out there, now we do!

NARRATOR: His acoustic tags may save lives,

allowing officials to close beaches

when a tagged shark is detected.

SKOMAL: We can tell where the sharks are

and when they approach popular swimming beaches.

And in some cases,

we've actually reached out to those areas to say,

"Hey, by the way, you've got a shark in your backyard."

NARRATOR: It's clear that seals

are attracting great whites to Cape Cod,

where the beaches are the backbone

of the region's massive summer tourist season.

A fatal attack could mean beach closures

and pit those charged with public safety

against those whose livelihoods depend on the crowds.

So far, here, sharks have become part of the landscape.

They even hold shark fishing tournaments,

which are controversial

because fishing for sharks, like these makos,

for sport, food and the shark fin soup trade

is devastating shark populations.

But they do offer scientists like Skomal an opportunity

to examine and take samples from specimens

that were swimming in the wild just hours before.

Two-zero-zero point eight.

The more we learn about sharks, the more we realize

how critically important they are to the marine ecosystem.

They fill a role of apex predator.

They control, in essence, the balance of the ecosystem.

So we really have to be very careful when we exploit sharks.

NARRATOR: While fatal shark attacks on humans are extremely rare,

every year, an estimated 100 million sharks are killed.

Among those who want to protect sharks is Wendy Benchley,

wife of the late Peter Benchley, author of Jaws.

BENCHLEY: Jaws tapped into a primal fear that all human beings have

of apex predators,

whether they're tigers or lions or sharks.

Fatal shark attacks around the world

are very, very rare, but when one does happen,

justifiably so, communities are very upset,

and the initial instinct always of a human

is to go out and kill whatever it is that is killing you.

Sharks are being finned and killed,

up to 75 million every single year,

just for shark fin soup,

and it is devastating the populations.

But of course, the solution is not to go out and kill.

We learned that we needed to keep our apex predators

to have an ecosystem that works,

and we need our sharks in the ocean

to keep our ocean healthy.

NARRATOR: In Western Australia,

sharks are a recognized risk for an ocean-loving public,

but interactions with great whites

are no less devastating.

ELYSE FRANKCOM: There's not a day that I haven't thought about it.

NARRATOR: Elyse Frankcom was a snorkeling guide

for tourists wanting to swim with dolphins.

FRANKCOM: I was diving under the water and came up for a breath,

and that's when I just felt this almighty whack.

The impact was just like getting slammed by a train.

I remember getting pushed out of the water.

I looked down, and that's when I knew what had happened.

My first reaction was, "Punch it, push it away."

The shark swam off, and I started sinking.

I was unconscious.

I remember taking my first breath.

As soon as they got me on the boat,

that's when the pain kicked in.

Very, very intense pain.

The shark cut right through my leg

and right down to the bone.

About 70 stitches on that side

and 130 or something on that side.

I had a shark tooth pulled out of my bone.

I had to learn how to walk again.

My mind is starting to play games on me now.

I'm starting to dream about sharks a lot more.

The longer I stay out of the ocean,

the more scared I get.

NARRATOR: The damage inflicted by a large shark can be devastating.

But most often, human victims survive the attack.

Why?

Steve Huskey is a functional morphologist

specializing in understanding how animals are built

and behave to capture prey.

He's studying the case of Robert Gumm,

who in 2011 was surfing with friends off the Oregon coast.

A great white attacked, slicing this chunk out of his surfboard.

Then it disappeared.

Gumm escaped without injury.

Was this a test bite

or a full-on attack that was aborted?

My curiosity's piqued

because I want to know exactly what happened here.

What does it take to cause that kind of damage to a surfboard?

NARRATOR: To find out, Huskey and colleague Chris Byrne

use a machine to measure the force

when a shark's tooth penetrates a surfboard.

This is the great white shark tooth.

That's right.

This is the perfect design for a tooth.

Nice triangular shape.

That point makes initial piercing,

slices its way through with those razor-sharp edges.

It looks horrible.

It looks beautiful!

Your machine is going to help us determine how much damage

and how efficiently this tooth

is able to go into that, correct?

BYRNE: That's right, right into the surfboard.

HUSKEY: So we'll have a way of determining the force

that was required to puncture a tooth into the surfboard.

And determine pressure.

We've got pressure right there.

So I'll bring it down

just to where it's about to make contact.

Perfect.

(creaking)

BYRNE: Can you hear it?

HUSKEY: I can hear it, snapping fiberglass.

Every serration is making more and more of a hole.

(louder creaking)

It sounds excruciating.

BYRNE: It's just sawing right through.

Let's take a look at the data.

Look how it rises right up to 20 pounds

before it even punctures.

That's our first puncture.

NARRATOR: 20 pounds of force isn't a lot--

a fraction of how hard humans can bite--

but focused at the tip of the shark's tooth,

it translates into massive pressure.

HUSKEY: If we look at the extremely exquisite

small part of the tooth taking 20 pounds of force

over that much surface area...

That tiny little area.

We're talking about thousands of p.s.i.

Absolutely.

NARRATOR: A large great white can bite 20 times harder than a human,

generating massive pressure

on the tip and razor-sharp edges of the teeth,

easily slicing into skin, blubber and muscle

like that of a whale or a surfboard.

Huskey's experiment shows that a shark's tooth

is incredibly efficient at penetrating its target.

HUSKEY: What it reveals

is that it doesn't take jack to bite through a surfboard.

NARRATOR: And what happened in the attack off the Oregon coast

becomes more clear.

HUSKEY: That was no exploratory sample bite.

I have complete faith that that attempt on that gentleman

off the Oregon coast was a full attack.

He was coming in for the kill,

and then something changed his mind.

In this case, it's got to be the fact that he bit something

that wasn't soft, chewy, fleshy, and didn't taste bloody.

NARRATOR: Huskey believes that sharks have a "feedback loop."

When they bite something, taste and touch tell them

whether this is a meal or a mistake.

HUSKEY: Contact on bone is probably something

that very quickly turns them away

from whatever they're trying to chew on.

They don't get that with a seal.

We're talking inches of blubber.

That's an entirely different motivation and sensation

than is something like a scrawny human bone.

In the event where somebody survives it, they were rejected.

They weren't good enough to be shark bait.

NARRATOR: The job of finding out how sharks sense us,

what triggers an attack,

and how to stop them before they bite

falls to Shaun Collin at the University of Western Australia.

What are your directions we've got with the rigs?

SHAUN COLLIN: One of the basic questions we're really interested in

is determining why a shark attacks prey versus a human.

What are the sensory cues it uses to make that decision?

It turns on his axis and he's gone.

NARRATOR: Collin's work delves deep into shark biology

to explore what sharks see, hear, smell and sense

in ways we're just beginning to understand.

His goal: test all the shark deterrents

currently on the market

and develop new ones based on groundbreaking science.

COLLIN: We want to get rid of the guesswork.

We want to base it on evidence that we can then rigorously test

and have statistical basis to rely on

to develop these deterrents and bring them to market.

NARRATOR: He's come here, the coast of Western Australia,

to a place with a well-earned name-- Shark Bay--

to test shark deterrents

based on years of research into the sensory systems of sharks.

COLLIN: Sharks are a major part of the marine ecosystem.

They've been around for over 400 million years.

They balance the ecosystem.

They're sensory machines

which are sampling their environment continuously.

NARRATOR: Sharks have senses like us: sight, smell, hearing and touch.

But they have other extraordinary senses

beyond our own.

They can detect weak electrical fields,

the Earth's magnetic field,

and minute changes in water pressure caused by passing prey.

Collin's laboratory research focuses on shark vision,

especially in the creature

that haunts our Jaws-inspired nightmares: the great white.

Great white sharks are ambush predators,

cruising deeper water to spot prey above them.

COLLIN: They see a silhouette of a human

but that casting of that silhouette,

high-contrast edges look a lot like a seal,

especially if it's on a surfboard

or a swimmer at the surface.

So if we can work out how a great white

visualizes its prey from below,

we've got a very good chance of preventing an attack.

NARRATOR: Collin pioneered the technique

of determining what sharks can see, and how well,

for the first time,

deconstructing how the great white targets its prey.

COLLIN: We've got a great white eye.

Probably an individual about two-and-a-half meters long.

NARRATOR: The structure of shark eyes is similar to our own.

With surgical precision,

Collin removes the retina from the shark's eye:

a thin, transparent hemisphere of tissue

containing light-sensitive cells called photoreceptors

and ganglion cells that transmit information to the brain.

COLLIN: A bit like peeling an orange.

NARRATOR: The more tightly the photoreceptors are packed

within the retina, the sharper the image.

COLLIN: Look at that!

That's the retina.

Carefully...

NARRATOR: Then, the transparent retina is stained with a purple dye,

making the cellular structures easily visible.

Counting thousands of minute photoreceptive cells

is a daunting task

made possible with a computer-controlled microscope.

The result is a map of the shark's retina

showing the density of photoreceptors

in different areas.

COLLIN: In this case,

the highest densities of cells

occur in this region of the retina.

NARRATOR: This part of the eye has the greatest ability to see detail,

contrast and movement.

That means that in the great white's field of view,

their sharpest vision is of objects above them.

COLLIN: This gives us a lot of information

about what part of the eye they direct towards eating prey.

NARRATOR: Great white sharks rely on vision to target their prey.

But other species rely more on their ability

to sense electrical fields or their sense of smell.

How can we tell which senses are of greatest importance

for different species?

Kara Yopak, a member of Collin's research team,

gets inside the shark's head, literally, to find out.

YOPAK: When you look at a brain, I can make fairly good predictions

about what that animal's eating,

how fast it's swimming,

the general environment that it's living in.

This is the brain of a great hammerhead shark.

NARRATOR: Hammerheads are open ocean predators,

living along the continental shelf

in tropical and warm temperate seas worldwide.

They feed mostly on fish.

YOPAK: Its regions of the brain for vision

are actually not very large.

This is likely not to be a very visual animal.

NARRATOR: Hammerheads rely on other senses,

like electroreception, to target their prey,

more so than the great white.

YOPAK: Here we've got the brain of the great white.

The regions of the brain that receive visual input

are quite large in comparison to other species,

as are the regions of the brain that receive smell.

But what becomes very pronounced in the hammerhead

is this protrusion here at the front of the brain.

And this is a region that we've associated

with what we call social intelligence.

So you see enlargement of this area in species

that form true schools, that aggregate by sex and size,

and that often have mplex courtship and mating rituals.

Whereas in the great white,

that region of the brain is not very pronounced,

which leads us to believe

that the great white is, in fact, a solitary hunter.

NARRATOR: There's another conspicuous difference

between the brains of these two species.

YOPAK: A lot of people are really surprised

when they see the brain of a great white,

particularly in comparison to the hammerhead,

because it looks so small.

But there's an amazing range of behaviors

that the great white's capable of,

and it's all controlled by this brain.

So there's clearly a difference

in the senses that these animals are relying on.

They all have the same battery of sensory systems,

but the relative importance of each of those systems

is going to be varied between species.

NARRATOR: While these sharks have the same battery of sensory systems,

there's clearly a difference in the senses they rely on,

reflected by which parts of the brain are enlarged,

clues to which senses to target for effective deterrents.

YOPAK: The idea of creating a blanket repellent

that's going to repel all sharks in the same way

really isn't realistic.

But when we're developing a repellent

for a great white shark,

we likely want to target the visual sense.

NARRATOR: If shark's eyes resemble our own,

can they see different colors, like us?

Collin thought that sharks, like some stingrays,

their close relatives,

would have color vision similar to ours.

For fish and humans, color vision is made possible

by three different types of cells in the retina

called cone cells,

each one responding to a different color:

red, green or blue.

In Shaun Collin's lab,

Nathan Hart uses a machine that measures what color light

the shark's photoreceptive cells are sensitive to.

HART: You can see here the beam

as it scans through from the UV to the red.

NARRATOR: What he finds in the shark species they've examined,

including great whites,

is that they only detect one color of light

in the green part of the spectrum.

Everything they see is in shades of that color.

For us, with no other color to compare,

it's like black and white.

COLLIN: We were very surprised

to find out that sharks were colorblind.

Two out of the three cone photoreceptors were missing.

So we only found a single cone photo receptor.

Now, this means

that they don't have the machinery within the retina

to process color.

NARRATOR: Collin believes this inability to see color

and a reliance on high contrast

are keys to creating an effective deterrent

for many species of shark.

The great white shark attacks in Western Australia

were an unusual series of events.

Collin and other shark researchers want to know

what factors could have triggered the attacks

and if there's a way to stop sharks before they be.

Shaun Collin is here in Shark Bay, Western Australia,

to test shark deterrents

that are already available to the public

and new ones he and his team are developing.

COLLIN: We've worked on lots of smaller sharks

in our laboratory tanks at the university.

But we've got to make that progression from the lab

to the wild.

NARRATOR: These metal frames are designed

to hold a bait canister to attract sharks,

along with the shark deterrent to be tested

and a pair of cameras.

COLLIN: The idea of having two cameras

is that we've got two different perspectives

on the behavior of the sharks.

NARRATOR: Collin's team preps the first test

with a device that emits an electric field,

powerful enough to shock a human if the electrode is touched.

COLLIN: This type of deterrent has a long electrode,

which is this lead here,

which extends for a couple of meters

typically behind a diver or the wearer,

and once turned on, creates quite an extensive

and fairly strong electric field around the device.

This is the other type of commercially available

electric device that we're going to be testing.

It's an anklet-style device,

again, worn by divers or swimmers.

NARRATOR: Bait canisters are filled

with a mixture of smelly, bloody ground fish...

and the electro-repellent rigs are deployed.

Each rig is anchored to the bottom

and suspended in the water column by floats.

They'll be left for two to three hours--

enough time, they hope, for the bait to attract a shark.

This is what happens when these rigs

are deployed without deterrents--

bites that would inflict serious wounds.

But which will be stronger,

the scent of food or the electric deterrent?

While the frequency of some electric fields

seem to repel sharks,

others attract them.

So, which frequencies make animals into targets

and which might protect us?

Ryan Kempster has developed techniques in the lab

to find out.

Bamboo sharks, small and easily kept,

hunt for prey hiding under the sand,

given away by the electrical impulses of their muscles.

So we know that all organisms give off bioelectric fields.

And these can essentially be measured.

NARRATOR: With every muscle movement, even the beating of a heart,

an electric field is generated.

KEMPSTER: The actual size of the organism itself

determines how far that electric field extends

in a water column.

So a larger animal is going to give off

a larger electric field.

NARRATOR: With electrodes attached to this acrylic plate,

which he buries under the sand,

Kempster simulates the tiny electric field

of the shark's prey: a small crustacean or fish.

With a camera mounted above the tank,

he records when the shark bites at the electrodes,

indicating it has sensed the electric field.

So just how sensitive

is the bamboo shark's electroreception?

KEMPSTER: They can sense down to around about one nanovolt.

Essentially, this is a billionth of a volt.

So it's an incredibly low electric field,

so they're really, really very sensitive

to the bioelectric fields of potential prey.

NARRATOR: Kempster measures the strength of the electric field

and the distance at which the sharks can sense it.

KEMPSTER: Oh, there we go.

That was a good one.

You can really see, it's really kind of this zone here

where they have to get within to react.

It's really a very close-range sense.

So they would typically use their other senses to hone in

on where the prey is,

and then it's really that last-minute feeding strike

they would use their electroreception

to assist them to locate that prey.

Oh, there we go.

NARRATOR: Electroreception is a short-range sense.

It's only when a big shark gets close

that its electro-sense locks on to a living target.

Electroreception can help sharks find prey,

but it can also warn them of danger.

Even these embryonic bamboo sharks

can respond to an electric field

that simulates the approach of a big fish.

We can see the shark breathing away very rhythmically.

Its tail is moving in the egg case

to help flush oxygen around the egg.

But then, as soon as we turn on that electric field...

Electrode on.

KEMPSTER: It stops breathing.

It stays really still, tail goes really still,

and this is essentially the response

to that electric field

that's mimicking the predator in the water.

Electrode off.

NARRATOR: Kempster has found the electric field

that disturbs bamboo sharks,

but is there a specific electric frequency

that will turn large sharks away?

He thinks that fding the right frequency of an electric field

is crucial to deterring dangerous sharks

like the bull, tiger and great white.

KEMPSTER: And this is really key

to determining how to create an effective repellent,

in finding out exactly what that frequency is

that they're most repelled by.

NARRATOR: Back on Shark Bay, the team tests other deterrents,

based on their research into shark vision.

This one is a flashing light.

They'll transfer the camera's footage

to the computers to watch later.

There you go, Dave, here is the cameras from rig 27.

This is the strobe lights.

Brilliant.

Let's see if we've had some luck this time.

NARRATOR: In the meantime, they've got another deterrent to test:

scientifically designed patterns for wetsuits.

This is designed to be camouflaged under water,

certainly to the visual system of a shark.

NARRATOR: As Collin and Hart discovered, sharks are colorblind.

They see the world in shades of black and white.

This material is designed to fade into the background

as the light changes at different depths,

each color tailored to what a shark's eye sees.

COLLIN: So the idea is,

the shark just swims by and has trouble seeing it.

That's right.

NARRATOR: A second design is very different.

HART: We've also got something

which has been suggested for a number of years

to be a good shark deterrent,

and that's a pattern that mimics a sea snake's coloration.

NARRATOR: Sea snakes are highly venomous,

and they advertise their toxicity with bold patterns

that warn predators to stay away.

COLLIN: Most sharks don't like eating things that are striped,

such as a sea snake.

It actually is a noxious animal to them.

NARRATOR: Collin thinks that many sharks naturally avoid stripes.

Again, the team's research into what sharks can see

is crucial to recreating the sea snake design

in the right proportions.

COLLIN: We had to actually work out the spacing of that pattern,

the bars or the stripes,

by our knowledge of the spatial resolving power

or the resolution of the eye.

NARRATOR: The underwater cameras run continuously.

For the scientists, finding that instant when a shark approaches

means scanning hours of footage.

Finally, their patience is rewarded.

(chuckling) Oh, that's cool.

NARRATOR: A bronze whaler, a shark known to attack humans,

has found the bait.

This test rig has the flashing light as a visual deterrent.

That's nice, isn't it.

He's got a little remora

following him on his dorsal flank.

NARRATOR: The shark makes five passes at the bait,

never getting too close, each time turning away.

These sharks are opportunistic feeders,

clearly interested in the bait,

but the flashing light seems to keep this one at a distance.

Well, it is certainly being deterred.

We can probably analyze this in slow motion as well

so you can time when the light is on

with how the shark reacts.

Absolutely.

NARRATOR: Next up, video footage from the test rig

with the anklet-style electrical deterrent.

Oh, look at that!

It's a hammerhead.

Wow!

NARRATOR: Hammerheads hunt with electroreception,

and they seem especially sensitive to electrical fields.

COLLIN: He came straight in!

Right towards the bait

and then almost did a 180-degree turn straight away.

HART: Yeah, looks like he was deterred, all right.

COLLIN: This is where the device was turned on

with the electric field extending out.

That was amazing.

NARRATOR: Finally, the bold, sea-snake wetsuit design

seems to turn another hammerhead on its tail.

He reacted almost instantaneously.

Did the same behavior.

Didn't get as close this time.

It was deterred from a greater distance from the actual device.

HART: Definitely keen on the bait.

NARRATOR: Their research seems to be paying off,

but to test their ideas on the most dangerous sharks,

they need to be in the right place at the right time.

COLLIN: Despite the spate of attacks that have happened

over the last year or so,

it is still inherently hard

to find large predatory sharks off our coastlines.

NARRATOR: For now, there is no one answer,

no surefire way to protect humans from attack.

COLLIN: We need more sharks interacting with our deterrents

before we can really

make any judgments about how effective they are.

NARRATOR: Halfway across the globe, on Cape Cod,

Greg Skomal continues to tag and monitor great whites

as they come close to the beaches where people swim.

That is going to be one hell of a shot.

NARRATOR: Chief ranger of the Cape Cod National Seashore,

Leslie Reynolds, and head lifeguard Keith McFarland

are on alert in a place where great whites are a new threat.

REYNOLDS: People are intrigued by the white shark.

They want to learn about them.

They would actually like to see one...

from the beach.

NARRATOR: Researchers are going further than ever before

to understand how sharks sense their world and hunt for prey.

COLLIN: There's no holy grail that we can see in front of us yet.

They are wild animals; they're hard to study.

But we really do feel that we can deter them from our beaches.

NARRATOR: That's the goal that these scientists are racing to achieve

to better understand these powerful predators

and try to save the lives of both humans and sharks.